The performance of an opto-coupler is highly dependent on process and assembly variations. One aspect of an opto-coupler that can be affected by process and assembly variations is its reference current threshold.
Sometimes, manufacturers attempt to control an opto-coupler's reference current threshold by carefully controlling the opto-coupler's process and assembly attributes (e.g., by ensuring that process and assembly parameters remain within specification).
Alternately, or additionally, an opto-coupler's reference current threshold may be trimmed at the wafer sort level. However, trimming at the wafer sort level does not account for process and assembly steps that occur subsequent to the wafer sort level (e.g., process and assembly steps at the packaging level). As a result, trimming at the wafer sort level can be of limited use.